Method of recovering blast furnace flue dust



Oct. 10, 1933. A. HASWELL ET AL 1,930,010

METHOD OF RECOVERING BLAST FURNACE FLUE DUST OriginfFiled May 14, 1931 s Sheets-Sheet 1 ARTHUR B. HASWELL FRANK G. CUTLE BY %a ATTORNEYS:

Oct 10, 1933. A HASWELL ET AL 1,930,010

METHOD OF RECOVERING- BLAST FURNACE FLUE DUST Original Filed May 14, 1931 3 Sheets-Sheet 2 INVENTORS ARTHUR B. HASWELL BQRANK G. CUT ER 7 /WF W AITORNEYS Oct; 10, 1933. A. B. HASWE LL ETAL 1,930,010

HETHOD OF RECOVERING BLAST FURNACE FLUE DIEST I Original Filed ui 14, 1931 3 Sheets-Sheet s INVENTORS ARTHUR B. HASWELL FRANK G. CUTL I? ATTORNEYS Patented Oct. 10, 1933 PATENT OFFICE LmTHOD-OF RECOVERING BLAST FURNACE FLUE DUST Arthur B. Haswell, Birmingham, and Frank G. Cutler, Ensley, Ala.

Original application May 14, 1931, Serial No. r 537,400. Divided and this application March 23, 1932. Serial No. 600,764

9 Claims.

This invention relates to metallurgy, and more particularly to steel metallurgy, and to a method of sintering and fusing finely divided metalliferous materials, such as blast furnace flue dust. Phis invention is 'a divisional application of application Serial No. 537,440 filed May 14, 1931 which is directed to the furnace apparatus devised for accomplishing the sintering and fusing of finely divided metalliferous material.

Blast furnace flue dust is comprised substantially of fine material of the blast furnace charge which is carried out of the top of the blast fur nace by the furnace gases. In every blast furnace producing pig iron, there is usually from 100 to 400 pounds or more of this fine material blown out of the furnace per ton of pig iron product produced. This material is of substantially the same general analysis as is the material utilized in the production of pig iron, except that it is of a very small particle size. If this material is col-- lected and charged back into the blast furnace it would either be blown out again or would pack down within the furnace so as toobstruct the free flow of gases therethrough, thereby causing trouble in the operation of the furnace.

Heretofore it has been customary to consolidate this blast furnace flue dust into larger sizes by agglomerating or by sintering the particles together by the Dwight-Lloyd or Greenwalt process, or in lime The agglomerated or sintered product thus obtained is unsatisfactory to recharge into the blast furnaces because the agglomerated or sintered particles readily disintegrate to form a relatively large proportion of fines which are again lost or blown out of the blast furnace.

One of the objects of the present invention is to provide an improved method for agglomerating finely divided metalliferous materials, such as blast furnace flue dust.

Another object is to agglomerate finely divided materials, such as blast furnace flue dust into a sintered and fused product.

Another object is to facilitate and to improve the recovery of the metal content of blast furnace flue dust.

Other objects and advantages may become apparent as the invention is more fully disclosed.

In accordance with the objects of the present invention, we have found that finely divided metalliferous materials may be sintered and fused in the following novel manner. The finely divided materials may be admixed in any convenient manner with finely divided materials capable of reacting therewith to form a fusible slag and the admixture fed preferably by air blast, through a high temperature heat zone maintained at a temperature sufiicient to effect 'a substantial incandescence of the individual particles of the admixture to approximately a Means are provided in the stack to introduce burning fuel, such as gas, oil, powdered coal and the like; and means are provided to introduce in the stack, preferably at the top, and preferably by air blast, the finely divided metalliferous materials in such manner that they pass through the hot temperature zone in the stack before falling upon the hearth. The temperature in the 0 stack is maintained suificient to incandesce the metalliferous particles at orto approximately the plastic stage and the temperature of the hearth is maintained at a temperature at or above the melting point of the slag admixture. This fur- 35 nace has also been designed to operate in conjunction with apparatus designed to utilize the excess heat energy of hot combustion gases, such as a boiler, or air preheater, or the like apparatus.

Before further disclosing the nature of the present invention, reference should be made to the accompanying drawings, wherein Fig. 1 is a sectional side elevation view of a type of furnace designed to accomplish the main object of the present invention;

' Fig. 2 is a cross-sectional plan view of the same;

Fig. 3 is an enlarged sectional side elevation view of the bottom part of the furnace;

Fig. 4 is a sectional side elevation view of a contemplated modification of the furnace illustrated in Fig. 1 when. utilized in combination with a boiler furnace; and

Fig. 5 is an enlarged sectional view of a type of slag screen utilized in the furnace of Fig. 4.

As a specific embodiment of the practice of the present invention we will describe the same as it, has been adapted to the sintering and fusing of blast furnace flue dust. This dust is.collected 110 in the art. Such finely divided metalliferous material comprises approximately 26% iron, 11% silica, 12% calcium oxide, and approximately 25% I 5 carbon, with the remainder comprised in part, of aluminum oxide, manganese and phosphorus compounds. The particle size varies materially, usually the coarser particles being comprised in the main of carbon, and the finer particles being comprised of the bulk of the iron. We have found that where the lime content of the material is relatively high, it may bereadily fluxed at a temperature approximating 2500 F. without the additionthereto of additional amounts of i5 fluxing material. In order to properly flux the material, however, the bulk of the carbon content thereof should be eliminated. We-have designed a furnace to accomplish this.

Referring to the drawings, Fig. 1, the furnace of the present invention, comprises substantially a refractory lined stack 1 supported on refractory base 16, having a water cooled shell 2, the refractory lining 4 terminating at the bottom into a slightly sloping hearth 5 leading towards a tap opening 6, from which the molten material on the hearth may be tapped into a conveyor 7. The products of combustion of the furnace pass out through stack 8 provided with a damper 9 to regulate the draft. A number of burners 3 disposed about the circumference of the stack 1 in the manner indicated are provided. Preferably the burners are gas or liquid fuel burners and are disposed so as to introduce the burning fuel tangentially to .the inner circumference as; of the stack and also preferably in a downward direction towards the hearth-5..

In the sealed top of the furnace, through pipe 10, the fine flue dust particles are fed from bin 11 by means of .a blast of air blown from fan 4o=;- 12 and under control of feeding mechanism-13. Bin 11 is supplied with theflne flue dust particles by a conveyer (not shown). Means, such as removable covers 14, are provided in'the top of the sealed furnace to give access to the interior of the furnace 1.- The operation of the furnace illustrated in Figs. 1, 2 and 3, in the sintering and fusing of flnely divided metalliferous material, such as blast furnace flue dust, may be briefly described as fol-.- 59 lows: By means of burners 3, which may be fed either with liquid, gases or powdered fuel, such as for example, natural, by-product, or blast furnace gases, or with oil, tar or powdered coal, the interior of the furnace is raised to a temperature approximating 2500 F. Into this furnace the finely disseminated flue dust is fed by the air blast coming ugh pipe 10, in the manner indicated. This ue dust may be of the same sub-- stantial composition as is obtained from thesblast furnace, or it may be admixed with proportions ofadditional carbonaceous material, or with proportions of additional fluxing materials, or both, as my seem suitable. By being introduced within the heated furnace in the manner indicated, the

as content thereof is ignited and burned to oxides of carbon and the inert iro silica, lime, and other materials areincandesced to a temperature at which they become, molten.

The relatively 'flne particle size of the flue dust mfacilitates the rapid and complete incandescence of the flue dust particlesto the fusion temperaature. The fused material collects in the bottom cf-the furnace upon the hearth 5, from which itisp'eriodically withdrawn through tap opening. 35 3 into conveyor molds 7.. Bypositioning the gas 7 1,980,010 in any convenient manner heretofore practiced burners so as toplay upon the'hearth the temperature thereof may be readily'maintained above the temperature at which the fluxing material fuses.

The bulk of the iron and the inert ingredients of the flue dust, is recovered in the fused slag product. The bulk of the carbonaceous material contained in the flue dust is oxidized'to carbon oxides andpasses out the chimney with the rest of the combustion gases. By water cooling the exterior of the furnace in the manner illustrated,

a relatively long life in the'refractory lining 4 is assured.

An alternative hearth structure is illustrated in Fig. 3, which may be briefly described as a continuous tap hearth, wherein the molten slag, as formed on the hearth 5,. overflows through lip opening 15 into the suitable molds or conveyers, where it is solidified a The slag product of this type of'fumace may be broken out of the molds into any desired particle size and charged back'into the blast furnace without the detrimentalresults attending heretofore agglomerated or sintered blast furnace flue dust particles. Being fused, it is not subsequently broken down into relatively fine products, as heretpfore sintered products have been found to do.

While we have disclosed the sintering and fusing of blast furnace flue dust, it is apparent that we are not limited thereby as the method disclosed is adaptable to the sintering and fusing of a wide variety of flnely' divided metalliferous materials.

In theafurnace structure of Figs. 1, 2 and 3, the hot combustion gases are permitted to pass out of the smoke-stack 8, without attempting to I utilize their heat content. In Figs. 4 and 5, we have devised and designed an apparatus wherein the furnace principle of Fig. 1 is utilized in combination with a boiler and chair preheater. Referring to the drawings (Fig. 4) the blast fumace flue dust sintering furnace 21, is connected with a boiler furnace 22, and an air preheater 23; in such manner that the heated gases from the sintering furnace, circulate first through the boiler furnace, and then through the air preheater furnace before passing out of the stack 24, thus absorbing in the water 'd air substantially all of the heat energy in the co bustion gases otherwise wasted in Fig. -1. The sintering furnace 21 is also ,shown as being lined with boiler tubes 25, protected with refractory brick- 26, from direct contact with the furnace flames. A slag screen 2'7, is provided, betweenthe sintering furnace and the boiler furnace to intercept the slag that no is carried along with the combustion gases passing from the sintering furnace into the boiler furnace. The fused slag collects upon the hearth 28, and may be tapped therefrom in a manner substantially as shown in Figs. 1,2 and 3. For this purpose a tapping hole and access door 29" may .be

provided. v

A gas burner 30 supplied with hot combustion air from header 31 supplied from air preheater 23 in any convenient manner, extends within the furnace 21. Into the current of gas and hot air, which has a relatively high velocity, so that an intimate admixture thereof is obtained, we feed the relatively flnely pulterized blast furnace flue dust from bin 33, which is supplied thereto by a conveyer (not shown), by means of a'blast of air from header 31, the feeding mechanism 32 being substantially identical with that heretofore described in Fig. 1. a

An external fan (not shown) blows air at 161 atmospheric temperature through the air heater 23 to the header 31, thereby supplying the gas burner with preheated combustion air. A damper 34 in the header 31, in the connection between the air header and the gas burner 30, regulates the air needed for combustion, and can be under the control of an automatic regulator (not shown), so that only the right amount of air required for combustion, will be admitted. In this manner, a relatively uniform high temperature sufiicient to melt the finely divided flue dust nace 22, where the bulk of the heatenergy con- I tent in the gases is given up to the water in tubes 36, thereby generating steam, and from the boiler furnace passes into the air heater 23, where the residual heat is utilized in preheating the combustion air. From thence, the combustion gases pass into the smoke-stack 24 and out of the top thereof.

The design of the slag screen is'illustrated in greater detail in Fig. 5, which is a cross-sectional plan View taken along line 55 of Fig. 4, wherein it may be noted that the screen substantially comprises a plurality of groups of tubes arranged as a baille to extend substantially across the flue opening. Water is circulating through the tubes, and, the fine particles of the flue dust being carried along by the combustion gases, tend to condense thereon. As the temperature of the gases is relatively high, approximating at the melting point of the flue dust particles, the'depth of the deposit of these flue dust particles that may collect thereon, is relatively low, the excess tending to melt and drain off from the tubes and collect upon the hearth 28.

Drums 40. and headers 43 are provided to connect the tubes 25, 2'7 and 36 in the stack furnace, slag screen and boiler furnace respectively into one system. Nozzles 41 and 42 provide means whereby steam is released from the system.

While we have shown and illustrated in Fig. 4 a specific type of boiler furnace, it is believed obvious that other types of boiler furnaces utilizing surplus heat in hot combustion gases as a source of heating energy, may be equally as well employed. It is also believed apparent that while we have illustrated a water cooled sintering furnace, a sintering furnace of the type illustrated in Fig. 1 may equally as well be employed. It is also believed apparent that other types of sintering furnace may be designed to accomplish the objects of the present invention.

There may also be many modifications and departures of the specific embodiment disclosed herein without essentially departing from the nature and scope of the invention as set forth in the following claims.

What we claim is:

1. The method of sintering and fusing finely divided materials, which comprises force feeding the material into a heat zone maintained, at a temperature suihcient to incandesce the particles at least to a plastic stage, and centrifugally projecting the incandesced material upon a hearth maintained at temperature sufficient to fuse the material.

2. The method of sintering and fusing finely diveded materials, which comprises feeding the finely divided material by a blast of air into a heat zone maintained at a temperature sufiicient to effect at least an incandescence thereof to a plastic stage, and centrifugally projecting the incandesced material upon a hearth maintained at a temperature suflicient to effect a fusion of the materials.

3. The method of sintering and fusing finely divided refractory materials, which comprises admixing the materials with flnely divided materials capable of reacting therewith to form a readily fusible slag, and thereafter force feeding the admixture into a heat zone maintained at a tem perature sufficient to incandesce the particles thereof to at least plastic stage, and centrifugally projecting the incandesced material upon a hearth maintained at a temperature suflicient to effect a fusion of the slag.

4. The method of sintering and fusing finely divided refractory materials, which comprises admixing the material with finely divided materials capable of reacting therewith to form a readily fusible slag, and thereafter force feedingthe admixture by means of an air blast into a heat zone maintained at a temperature sufiicient to incandesce the particles thereof to at least a plastic stage, and centrifugally projecting the incandesced material upon a hearth maintained at a temperature suflicient to effect a fusion of the slag.

'5. The method of sintering and fusing finely n divided blast furnace flue dust, which comprises force feeding said dust particles into a heat zone maintained at a temperature-sufiicient to incandesce the particles to at least a plastic stage, and centrifugally projecting the incandesced particles upon a hearth maintained at a temperature sufficient to fuse the same.

6. The method of sintering and fusing finely divided blast furnace flue dust substantially free of contained carbonaceous material, which com-= prises force feeding the dust particles by means of an air blast into a heat zone maintained at a temperature sufficient to incandesce the inert components thereof at least to a plastic stage, and centrifugally projecting the incandesced particles 1245 upon a hearth maintained at a temperature sum-'- cient to fuse the same.

7. The method of sintering and fusing finely divided blast furnace flue dust substantially free from contained carbonaceous material, which 5 comprises admixing the dust with finely divided material capable of reacting therewith to form a readily fusible slag, and then force feeding the admixture by means of an air blast intoa heat zone maintained at a temperature sufflcient to 35 incandesce the inert components of the admixture at least to a plastic stage, and centrifugally projectingthe incandesced particles upon a hearth maintained at a temperature sufficient to fuse the same.

8. Themethod of sintering and fusing finely divided blast furnace fluedust substantially free of contained carbonaceous material, which comprises force feeding the dust particles by means of an air blast into a heat zone maintained at a 145 temperature sufiicient to incandesce the inert components thereof at least to a plastic stage, centrifugally projecting the incandesced particles upon a hearth maintained at a temperature suflicient to fuse the same, and thereafter recovering 1 0 the used material from the hearth in any convenient manner;

2'9. The method of sintering and fusing finely candesce the particles thereof to their approxi-* mate melting points and centrifugally projecting the particles upon a hearth maintained at a temperature substantially above the melting point.' v 

